Ford Repair: Ford F150, ford f150, fuel filters

Question
Hi,
I have a 2007 V8 F150.  I'm having a problem trying to figure out why my truck is making a straining sound sometimes when the rpm's
are between numbers 1 and 2 or the speed is between 30 and 40 mph.
It does it ever so often and may last a couple of hours or maybe all day and as fast as it started it'll stop and maybe not do it again for a week or so.  I've replaced the air and fuel filters and checked all of the fluids.  There are no check engine lights on.  Any suggestions?

Thank you

Answer
Denise, it could be coming from a belt.  You might need to change it.  To test it, next time it happens, open the hood while the car is running, through some water on the belt.  And if the sound goes away, then the belt is getting loose where it is slipping on the pullys.  Thanks!